text:
Why are on-board computers allowed to change controls without notifying the pilots?
Recently we've had the 737-MAX debacle, where it increasingly appears that the MAX on-board MCAS system repeatedly would issue nose-down events, leading to the Lion Air crash, and possibly another

On the Lion Air flight, when the MCAS pushed the jet’s nose down, the captain pulled it back up, using thumb switches on the control column. Still operating under the false angle-of-attack reading, MCAS kicked in each time to swivel the horizontal tail and push the nose down again.

Apparently there is a notification light for MCAS that was an optional package but will now be required.
It reminds me of two other incidents that lead to crashes

Air France 447 A330 - A frozen pitot tube caused the computer to switch to Alternate Law 2, which meant that the computer would no longer prevent dangerous flight inputs. While not the same as the MCAS issue, it lead to confusion of the cockpit crew (who had been making maximum nose-up inputs while at TOGA power), and thus the plane crashed due to stall. It was noted that there was nothing direct to alert the pilots that the switch had occurred.
Scandanavian Air 751 MD81 - Ice accumulated on the wings. When the plane took off, the ice fell off, striking the engines. The pilots noted the engines were surging and reduced the throttle, but an auto-throttle system not disclosed to the pilots kept increasing power back to full, thus causing engine failure and a crash landing.

Has anyone ever stated why aircraft systems are allowed to make changes without notifying the pilots? Is it something that just hasn't been a large enough problem to address until now?

The AF447 flight had an alternate law indication available to the pilots, as well as many other (too many in fact) warnings that caused further confusion. In automation systems, the key is to present the appropriate information without overwhelming the operator with too many conflicting or confusing warnings. AF447 showed that a pilot in the face of too much information will ignore everything the system is telling them and fly with how they think the aircraft should be flown.

For most modern aircraft, it is a design feature that some intervention is invisible to pilots. The rudder has automatically made invisible small adjustments to maintain symmetrical flight and dampen yaw oscillations for at least half a century, and more modern aircraft alleviate turbulence or other small disturbance from trimmed flight without announcing this either, as that would quite quickly become a nuisance...

I guess the question to ask is rather not “why don’t all automatic inputs get announced” (as quite often that’s actually OK) but “why would anyone design an automatic that is associated with a risky edge of the flight envelope and then not tell crew about its existence” (because that’s not OK).

The problem is computer systems designed by people with a computer science background, rather than by people with a background in aviation. Computer scientists will add safety subroutines as a matter of course, lacking the necessary judgement of an experienced pilot, ignorant of the fact that information overload is bad for the pilot when reaction time is at a premium. Excessive application of safety systems hides the crucial warnings from the pilot, who may be unable to eliminate the unimportant ones in the available time. This is a design failure, and cannot be cured by pilot training.

@Ed999 the requirements for the MCAS system would have come from someone with experience designing aviation systems. Plus, most people working in DO-178 driven projects are quite aware of the domain in which the software is running. Whether the indication of operation is provided to the pilot is a human factors decision, not one of software.

Indeed.  In AF447, the fool copilot that got them all killed was pulling all the way back on the stick. Normally you do that to maliciously stall the aircraft and kill everyone, and had he done that in a Boeing it would've been considered mass murder.  But the copilot had learned that if you do that on an Airbus, Normal Law will intervene to stop you.  He had become trained to avert stall by inducing stall to force Normal Law to fix it.  Unfortunately his plane was in Alt Law 2.

SelectStriker2 appears to be advising that this is human error (of the systems designer), while Harper appears to see it as both human error (of the co-pilot) and a design flaw (in not alerting him that the system was in Alt Law 2), and I view it as a (different) design flaw. Is there any consensus as to which it is? The first step in resolving the problem is surely to decide whether the computer system is flawed, and (if it is not) to then decide whether the pilots understand it.

I'm saying the infamous Mulhouse demo mis-taught pilots that wrong control inputs will cause right control outputs.  Airbuses teach pilots to fly badly and let big brother fix it, as a matter of routine.  The design flaw is there.

There is a general design principle, that some, but not all, of the behavior of the flight guidance system or autopilot should be visible to the pilot.  Usually automatic engagement or disengagement of a control system is indicated, but sub-modes of these controls or manual changes might be unindicated. That sounds simple and logical, but in reality it's a complex and tricky human factors issue. Displaying too much information to the pilots is just as bad as displaying too little, as too much information can cause them to ignore the most important indicators, like a stick shaker warning about a impending stall.
I know this isn't a very satisfying answer, but it's hard for anyone other than a human factors expert to answer a very general question like this with hard-and-fast rules.
For example, many autopilots will skip the aural warning about disengagement if the disengagement was directly caused by a pilot action. The pilot in this situation only gets a visual indication that AP has changed behavior. This sounds perfect, but on Aeroflot Flight 593 a pilot let his child into the cockpit, who then applied enough pressure on the yoke to disengage the automatic aileron control. There was no warning chime because the disengagement was considered intentional by the autopilot. This was unlike previous planes the pilot had flown, which contributed to the pilot's confusion when the plane began to turn and then go into a sharp bank.
The indicator light you mention for the 737 Max Lion Air crash is for "AoA disagreement", not MCAS engagment as you suggest.  While these kinds of AoA indicators are generally considered good ideas, it's still an area of debate how much they'd help confused pilots like in the Lion Air crash or the Air France 447 crash.
Similarly, the quality of indication was not the biggest cause to the accidents you've listed. For example, the Scandinavian Airlines Flight 751 could probably have returned to the airport successfully, but a compressor stall due to ice striking both engines at low altitudes is a bad situation no matter the auto-thrust behavior. Bad sensors and confused pilots can crash a plane with perfectly designed indicators.
Edit:  since this answer is getting a lot of attention, I think it's important to note that I don't really cover any special considerations for the edge of the flight envelope, auto-trim vs auto-disengagement vs changing sub-modes, or idiot-proofing of flight systems. I'd love to see this covered in more detail by people with experience.

That's a good point. Information overload is a very real problem.

I seem to recall a deluge of contradictory and confusing system messages being an issue in Qantas 32. Thankfully, the pilots were able to work through that one and get the plane in the ground mostly in tact (aside from the bits that had blown off the engine and wing when the turbine disc exploded,) but I seem to recall hearing the pilots talk about how many superfluous system messages they had to wade through in order to get to the important information of "an engine blew up, another is uncontrollable, and there's a hole in the wing."

There’s an argument to be made for a flight engineer to wade through all of that stuff, but that stuff is there to replace the flight engineer in the first place. Go figure.

There are two types of autopilots, one for the behaviour around the CoG and one for control of the CoG, as mentioned in this answer. Also sometimes called Inner Loop and Outer Loop. In short:

The F-16 is aerodynamically unstable and has a rapid control system that applies control surface deflections to provide artificial stability. This is done to make the aircraft extremely manoeuvrable. The pilot is deliberately kept unaware of all these rapid control deflections, to them it just appears as if the aircraft is stable. Inner Loop autopilots provide no feedback to the pilots, by design.
The automatic pilots that can be set in order to fly to a certain setpoint are Outer Loop control systems. By design, they do provide feedback to the pilot as to what they are doing, so that the pilot can feel and see what sort of inputs are given and can override them if they deem them to be incorrect. The A320 has no means to move the stick, so this feedback cue is unavailable and attention is demanded by alerts.

This article explains the design philosophy of the MCAS system: it was meant as an auto-stabilising feature in a flight state outside the normal envelope - the circumstances Inner Loop control is normally applied in.
So to answer your question: yes, some flight computers do change control surface deflection without notifying the pilots.

This is exactly the cause. The B737 used to be aerodynamically stable, but the forward re-positioning of the engines narrowed the space of stable flight parameters so much that a software interference was designed so that it would feel and behave the same even though its aerodynamics had changed. (For some context see https://www.latimes.com/local/california/la-fi-boeing-max-design-20190315-story.html.) The F16 comparison is spot-on. Hiding this interference is the whole point. Designing it to be invisible surely was the reason it was not even included in the training and manuals.

@PeterA.Schneider Fully agree there, and I can see the point of not including MCAS in the curriculum if it was designed for those circumstances. That leaves the question why one single faulty transducer can cause the system to engage in normal flight envelope states.

In the case of MCAS and the stabilizer control, there is "notification" that the stabilizers are being automatically adjusted in the form of the two wheels on either side of the thrust controls. They spin, have markings, and are very noisy, so the pilots could not have been unaware of them acting. The problem was that the pilots were (apparently) unaware of the possibility of turning off the automatic stabilizer inputs from MCAS and kept trying to manual override the MCAS/stabilizer adjustments. The switches to turn off the stabilizer inputs are right in front of the thrust controls on the co-pilot side.

They were also unaware of that specific trim function sponsored by MCAS which probably wasn’t particularly helpful in fault diagnosis.

Well, the actual position of the trim surfaces is plainly displayed right next to the Annoying Clackey Thing.  If they even looked to see where the sound was coming from, they'd be going "wow, that's an awful lot of up-trim", that explains the heavy yoke".   Then when they trimmed it back, they'd hear Clacky Thing again and "Enough!" switch off or just stop the trimwheel with your knee. It really looks like more a problem of green pilots who have spent all their flying hours pushing buttons on highly automated airplanes.  The automation cocks up at all, and they have no idea what to do.

@Harper "that explains the heavy yoke" I've had that happen to me during a training flight when the instructor (very likely inadvertantly; this was from rather touch-sensitive buttons on top of the shared control stick) changed the trim setting to, IIRC, full nose down. My first reaction when taking the controls back and trying to maintain level flight was along the lines of "damn, that's heavy!". Despite having only like 15-20 hours at the time, my first reaction beyond the immediate need of establishing positive control was to look over at the trim, and sure enough it indicated an extreme.

"the pilots could not have been unaware of them acting". However, the Speed Trim System also adjusts the trim automatically. So they could have very well thought it was the STS adjusting the trim, which is relatively harmless.


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What is the smallest aircraft to have a CVR / FDR?
I was wondering what is the smallest aircraft to have a CVR (Cockpit Voice Recorder) and/or FDR (Flight Data Recorder)?
Small single engine prop can sometimes have the avionics, like the G1000, that records some of the flight parameters on a memory card. But what about a proper CVR or FDR?
I'm not asking about military aviation, but more about general or small commercial airplanes.
I understand that it depends of the type of operation, but what is the smallest airplane to have a CVR/FDR on board?

By "proper" CVR/FDR do you mean a unit that meets crash survivability standards? Are you asking about recorders as required equipment or whether they are available as an option? As to when they are required, this question gives answers for FAA. As far as optional equipment that doesn't have to follow all the parameters set out by regulations then you can probably install recorders on just about any aircraft.

@TomMcW Yes, it would be a unit that meets crash survivability standards but that is not necessarily required. An operator can choose to have such equipment without being legally required to. If it's required on this type of aircraft or not that's another story.

Looks like in the EU as well as in the US the Cessna CE-510 Mustang needs one according to the minimum equipment list.
In the EU

-70-01
*** Cockpit Voice Recorder (For Combined Voice Data Recorder, refer to 31-30-01)

And in the US

-30-01
*** Flight Data Recorder (FDR) System

That is a 6 seat plane, you will be hard pressed to find something smaller although other similar in class aircraft may also have them.
It looks like some versions of the Cirrus SR-22 include an Aircraft Data Logger but im not sure if that conforms to the various impact regulations for a black box.

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text:
Can a SIGMET last less than initially forecasted?
Lets say I have a SIGMET that says VALID 310800/311200.
Is it possible that by 1100 the SIGMET would not be active anymore or it will always be valid until the published end time?

Yes, SIGMETs can be cancelled.
A quick web search uncovered, for example, the ICAO Asia/Pacific Regional SIGMET Guide, 6th edition, May 2017, which on page 3-16 (PDF page 24) says, in part:

3.5.4. Cancellation of SIGMET
3.5.4.1. Annex 3, 7.1.2 requires that "SIGMET information shall be cancelled when the phenomena are no longer occurring or are no longer expected to occur in the area”.
3.5.4.2. As such, it is mandatory for an MWO to cancel any SIGMET that is currently valid but for which the specified phenomena no longer exists or is expected to exist.

It appears that the cancellation is communicated with a new SIGMET, valid until the expiration time of the original SIGMET, specifying "CNL SIGMET XX" where XX is the original SIGMET sequence number. Sections 3.5.4.3 and 3.5.4.4 specify the format of the cancellation SIGMET. MWO is shorthand for Meteorological watch office.
SIGMETs can also be amended or corrected after issuance.
From the same document, the very next section, snipped for brevity:

3.5.5. Amendment/correction of SIGMET
3.5.5.1. If it is known that an existing SIGMET no longer accurately describes the existing or expected future evolution of the phenomena a new SIGMET, correctly describing the hazard should be issued, followed immediately by a cancellation of the original, erroneous SIGMET. [...]

So it is entirely possible that on the 31st at 11:00, the SIGMET originally issued with a validity of 310800/311200 is no longer in effect.

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text:
Can a non multi-engine rated pilot get a complex endorsement in a multi-engine aircraft?
I was wondering if a pilot with only an SEP can get his/her complex endorsement in a multi-engine aircraft? I would guess not but since I didn't find any clear info or FAR that sates you can't, I just wanted to be sure.

I think you are asking if a SEP pilot can receive training in a multi engine aircraft to fulfill the requirements of a complex aircraft endorsement without fulfilling the requirements of the multi engine type endorsement. I assume that would mean demonstrating operation of the flaps, retractable gear, and controllable propellers without demonstrating single engine operations. That is an interesting scenario.

@MikeSowsun That's exactly what I'm asking, sorry if it wasn't clear. And yes, its an interesting scenario indeed. From a logical standpoint I don't even know if it makes much sense but I couldn't find any regulation on the mater.

If the airplane meets the definition, which almost all multi-engine pistons will, then you can get your complex endorsement. There is even one training center that advertises getting your multi and complex at the same time.

§61.1   Applicability and definitions.
Complex airplane means an airplane that has a retractable landing
  gear, flaps, and a controllable pitch propeller, including airplanes
  equipped with an engine control system consisting of a digital
  computer and associated accessories for controlling the engine and
  propeller, such as a full authority digital engine control; or, in the
  case of a seaplane, flaps and a controllable pitch propeller,
  including seaplanes equipped with an engine control system consisting
  of a digital computer and associated accessories for controlling the
  engine and propeller, such as a full authority digital engine control.

§61.31   Type rating requirements, additional training, and
  authorization requirements.
(e) Additional training required for operating complex airplanes. (1)
  Except as provided in paragraph (e)(2) of this section, no person may
  act as pilot in command of a complex airplane, unless the person has—
(i) Received and logged ground and flight training from an authorized
  instructor in a complex airplane, or in a full flight simulator or
  flight training device that is representative of a complex airplane,
  and has been found proficient in the operation and systems of the
  airplane; and
(ii) Received a one-time endorsement in the pilot's logbook from an
  authorized instructor who certifies the person is proficient to
  operate a complex airplane.

Complex Airplane Endorsement
Learn to fly aircraft with retractable landing gear, controllable
  flaps, and a controllable propeller using our Piper Seminole PA-44-180
  airplane. You can earn your complex endorsement, or combine your
  training to earn your complex endorsement and multi-engine rating.*

Your last paragraph appears to be a quote, perhaps from the site linked above it, but isn't quoted. If it's not a quote, then it sounds like advertising for... something.

This doesn’t really answer the original question:  “Can a SEP pilot receive training in a multi engine aircraft to fulfill the requirements of a complex aircraft endorsement without fulfilling the requirements of the multi engine type endorsement.” This would mean demonstrating operation of the flaps, retractable gear, and controllable propellers without demonstrating single engine operations.

@MikeSowsun Not sure why it doesn’t answer the question. 61.31 says that you need training in a complex airplane. If the FAA wanted to restrict you to single engine, they would say so. There are several places in Part 61 where they use the restriction “aircraft category, class, type (if required)” so if they wanted to place restrictions on the type of airplane you can get a complex endorsement in, they certainly know how to do it.

I guess I just wanted to see it spelled out: “Yes, you can do your Complex Aircraft Endorsement in a multi engine aircraft without demonstrating engine out proficiency.” Your answer implies it, but doesn’t really say it.

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text:
How do I pay fees if I don't even land at the airport?
So let's say I'm going from Wellesbourne (EGBW) to Coventry airport (EGBE) and at Coventry I do 1 ILS approach and go missed and return back to Wellesbourne.
Even though I never put a wheel on EGBE how will they collect the fee for doing the ILS approach? (Yeah I know... you gotta pay for an ILS approach... yuk.)

Looking at http://www.coventryairport.co.uk/downloads/fees-and-charges-2017.pdf, I see that it refers to "EC Regulation EC 785/2009". I'm fairly sure that regulation is about skimmed milk powder. :) Anyway, there are also "Circuits [and Touch and Go’s]" charges.

So if you go missed and make a second approach are you charged for two approaches?

Welcome to Europe, where stuff isn't allowed to be free.

@GdD It's not free in the US either. Joe Citizen, who has never stepped foot in a plane, pays for a PPL to shoot an approach through his taxes.

I fly in France and I had the same question. Apparently they use the aircraft registration to identify the owner. If you rented the plane from a club or renting company, the bill is going directly to them, otherwise they are going to try contacting you. If for some reason they didn't get your registration or if the airport was uncontrolled then you don't pay the fee. That's how it works over here, however I can't say if the same would apply in the UK.

Ah right, it seems like it would be the same, thank you!

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text:
Where can I find info or techniques on calculating the influence of a duct on the thrust and efficiency of a propeller?
I am trying to run numbers on a concept VTOL fixed-wing aircraft, and I am looking at having fans or props positioned inside the wings, (which would therefore make the wings relatively thick for a fixed-wing aircraft). Naturally this would see the fans/props enjoying the benefits of a duct, but with minimal downsides such as the need to add weight/material as the wing is already going to be there.
I am using Blade Element Theory to trial propeller dimensions/numbers to see what kind of sizes I would need to achieve the VTOL (if I can minimize the radius of the VTOL fans then I can the wings thinner or with a smaller chord), but I don't know of any way to estimate the influence that the duct would have on the final thrust/power values.
If there is a rule of thumb for this, or a database, or some equation or anything, that would be a great help!

do these help you? https://aviation.stackexchange.com/q/27416/1467 https://aviation.stackexchange.com/q/9940/1467

Ducts offer improvements at low speed efficiency, "free" props better at higher speeds.  There are graphs on this site, which also include fan jets and turbo jets in the subsonic range.

There is info on power computations for ducted propellers in J. Gordon Leishman, Principles of Helicopter Aerodynamics. The beneficial contribution of the duct can be found in section 6.10.1 Fan-in-fin Design, and in section 3.3.10 Prandtl's Tip-Loss Function. In short:

If the duct is designed to prevent wake contraction, extra thrust is generated and less power is required to drive the propeller. The effects are computed with momentum theory, which is a simplification. For thrust T and power P, with $T_D$ and $P_D$ = ducted, $T_U$ and $P_U$ = unducted, $a_w$ = ratio of outlet/propeller area.:

$$\frac{T_D}{T_U} = \frac{1}{2a_w} \tag{1}$$
$$\frac{P_D}{P_U} = \frac{1}{\sqrt{2a_w}} \tag{2}$$

Tip loss. The duct prevents circulation loss at the tip if the clearance between tip and duct is small enough. Prandtl has been working on this in 1919 using momentum theory, an example for an untwisted blade is depicted below.

There is also this masters thesis, with measurements of small ducted rotors with low tip speeds.

Hindawi Publishing Corporation
International Journal of Rotating Machinery
Volume 2012, Article ID 474785,
11
pages
doi:10.1155/2012/474785
Research Article
Open-Water Thrust and Torque Predictions of a Ducted Propeller
System with a Panel Method
J. Baltazar,
J. A. C. Falc
ao de Campos,
and J. Bosschers


text:
How could the B-29 bomber back up under its own power?
I was watching some footage of the Enola gay

I was interested in the part where the plane was backing up over the bomb (starts around 18:27). It appears to be doing this under its own power with the propellers running. Could the B-29 reverse some propellers to do this?

https://aviation.stackexchange.com/questions/7689/why-dont-planes-have-a-reverse-propeller-as-air-brakes

@ymb1 Check out Mike's answer. He actually found a video with the props shown reverse pitching, along with landings done using only reversible props. I'm guessing it was to facilitate them landing on those shorter south Pacific SeaBee runways

@ymb1: Most B-29s didn't have reversible-pitch propellers.  The Silverplate B-29s (the nuclear-weapon-delivery version), however, did.

I watched a special on the island they flew out of to drop the bombs , the planes had to back over the bomb pit , to load the massive bomb, ,crazy they showed the wiring harness to a bomb they found on the island , they went back to it in a documentary and they had a scientist that was there. Answering questions for them . My wife's grandfather was a Dr at Hanford building it , he always said he couldn't talk about what he did even to my wife .

Some B-29s had reversible pitch propellers. All the B-29s used for the Atomic bomb missions had reversible pitch propellers.
Wikipedia B-29 Variants

Moreover, engine packages changed; including the type of propellers and range of the variable pitch. A notable example were the eventual 65 airframes (up to 1947's end) for the Silverplate and successor-name "Saddletree" specifications; built for the Manhattan Project with Curtiss Electric reversible pitch propellers.

Army Air Forces tests reversible propellers for B-29 bomber

What is the logic behind requiring reversible pitch propellers for the Manhattan project?

Although I can't find direct hard documentary evidence, I'll make the case that that B-29 has Curtis Electric reversing propellers thusly:

We know that Curtis had a reversing version of its electric propeller during WWII because the Consolidated had them for the inboard engines of the Coronado flying boat.
The B-29 in the video is clearly backing up under its own power, and you can tell at least two engines are higher RPM from the blade strobing.  It's not the wind blowing it back.  The B-29 had a free castering unsteerable nose wheel and you can see that steering is being done by ground crew manhandling a towbar for fine steering, probably assisted (or hindered) by bits of braking by the pilot.  Looks like a pretty tricky task.
There were many field mods done on the B-29 and things like installing reversing props in the field as an upgrade would certainly have been done late in the war.  And you can bet that Enola Gay had all of the latest and greatest field mods.  As field mods they were probably covered by Flight Manual Supplements and that sort of documentation can be very hard to track down.

Many planes have props that can be set to a negative angle, for braking during landing.  So, that could also be used to reverse under its own power.


text:
When flying a glider in emergency situation, would it be more safe to bailout or to land in a forest?
Is there any consensus when it comes to this question? If it depends then it depends on what exactly? I'm interested in the decision making in this kind of situation.

Do you have a parachute? Most glider pilots do not...

Yes, I'm assuming having a parachute in this question - in my country chute is obligatory.

Partly related questions: here, here

What exactly is the emergency? Are you making a controlled approach to the trees or uncontrolled?

Actually both situations are interesting, because you never know in which one you will end :) .

@RonBeyer: Modern glider seats are designed for parachutes. Certification regulations require that the seat design must allow the accommodation of a parachute worn by an occupant (JAR 22.785). If you don't wear a parachute, you will need a thick cushion to sit properly.

@PeterKämpf Interesting, the local glider club doesn't use parachutes, maybe it's just an EASA thing?

@RonBeyer: The seats are designed for parachutes. Even if they are not required it makes sense to wear them (and repack them regularly).

+1 to Ron's observation.  The glider club I used to frequent would only issue a parachute if you asked for one.  It would bee seen as odd to take a 2-33  (or similar) up wearing a parachute.  May just be a USA thing.

In EU are parachutes mandatory (as far I know in most of the countries) and  When having midair collision with structural damage, you have no option (http://www.dailymail.co.uk/news/article-2713010/The-amazing-moment-glider-pilot-bail-aircraft-parachute-safety-wing-fell-dramatic-mid-air-collision.html) when you're with stacked altimeter, it looks much safer to land anyway :P

In the UK we all have to wear a parachute. While learning to fly I asked my instructor if we have enough height for the chute to fully deploy before we hit the ground. His answer was No, but it makes finding the body easier if you have a big nylon flag attached. This from the guy when I was on a final approach and coming in a bit too steep said "Remember that you are flying a self-burying fibreglass coffin"

@AndyW: That particular problem would be easily solvable by using a ballistic parachute (one where the parachute is blasted out of its container rather than having to catch the air on its own), like the airframe parachute on a Cirrus except smaller.

Thankfully, I never had to make this choice. In my training I learned to stay in the plane and flare at the height of the treetops, then let the plane sink into the branches and have them stop and suspend the aircraft. The fuselage is quite effective as a protective shell, and up on top the branches are thin and flexible.
Use the parachute only to hoist yourself down from the stricken plane, if necessary.

Two-seater after landing in trees at Boberg glider port (picture source)

Nice picture!  Were they able to use the glider again?  Totally agree with that conclusion; from the numbers of paratroopers I've talked with (having dropped quite a few), it's clear that a tree landing in a parachute can be pretty rough on the parachutist, especially one wearing typical glider flying shorts & t-shirt, rather than a soldier's protective gear.  Tree landings were nobody's idea of a good time, even among those who had training & equipment to deal with them.

@RalphJ: I found the picture via Google, so I do not know much about that specific incidence. It was in a newspaper and it was mentioned that both instructor and trainee were distracted by the low sun and did not see the trees soon enough. From the picture I would guess the glider needed only minor repairs. However, with wingtip contacts there is always the risk that the spar root was damaged - this would be more serious.

The most common reasons for having a parachute on a glider is that the flight will involve aerobatics and / or extreme weather which could result in structural failure. For the vast majority of tows I have provided, aerobatics are the primary reason for wearing a chute.

@mongo: I know too many cases of mid-airs in a thermal to agree. Wearing one doesn't hurt.

Sadly, that does happen.  Amend my comments that chute wearing increases during competitions as well.

Regarding midairs in a thermal, it is beautifully written about by R Bach in Bridge Across Forever. (You pilots have to read through a few sissy chapters about romance stuff before getting to the gliding chapters :) )

@mongo: in every competition I was involved and/or know of, the chute was mandatory.

How did they do that without breaking the wings off the glider and hitting the ground like a giant lawn dart?

@Sean: The twigs and branches decelerated the glider gently, so when it dove down, it did so in slow motion.


text:
What is this weapon spotted at an airshow in South Africa?
I was at an airshow in South Africa, and they had this trailer sitting about.  No one knew what it is.

Those little red plates all say "warning, high voltage".  Those buckets are open at the bottom, and made of aluminium.

These finned pointy things are hollow, not sure what they are made of.  Were not solid plastic, but didn't look like fiberglass either.
A couple of specific questions:

What is it?
If the hollow things are covers, why are they so oddly shaped?  And if they are covers, why do they share features with liquid tanks?
Why are there half a dozen "High voltage" stickers attached?
What are those bins and chains?

it's an AA system and the hollow things are covers that protect the missiles underneath. I'm not completely sure this is on topic, but I'll leave the decision to the others.

@Federico Quite difficult to say if it is on topic or not. If this is a AA system, it is closely related to militarty aviation and could be accepted here.

Or you could say that it is off topic because it is “anti” aviation?!  ;)

It's a British Tigercat short range surface to air missiles launcher system. The cones are protective weather covers for the missiles which are removed prior to launch.
As to the 'buckets and chains' I'd venture a guess that they are a device to deflect and dissipate the rocket blast during launch but I am not totally sure. But they can be seen on YouTube (at 0:07 and 0:39).
From YouTube, on the right the blast being deflected up/down.

You can see the "buckets" deflecting the rocket blasts in a few frames around 0:07 of https://www.youtube.com/watch?v=qLwXYNF2VdM, and again for a bit longer at 0:39.

@JasonC I hope the pilots has already bailed out of those aircraft...

I guess the wire mesh, which is tightened by springs, is to protect from anything not gas in the exhaust.

I am amazed by how short those missiles are.  I think that is why everyone disregarded it as a SAM

In Britain it's a Tiger Cat and in the South African defense force it was called a Hilda missile system. I operated one when I did national service there.
The missiles are connected to a firing console via a thick cable. In the console you have a missile controller and computer operator. The missile controller controls the missile with a little teet (joy stick) and binoculars (laugh), an old war weapon.
Best effect of the missile was head on with the plane. If it was fired from behind it would never catch the plane as the missile was too slow.
We had an upgrade called a Cactus missile system.

Further to previous answers, the "chains and buckets" are to catch an umbilical cord which otherwise would coming flying backwards at launch. The missiles are indeed outdated, large and slow but that means the pilot can see it coming and it is enough to put him/her off their aim!!


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Is there a regulation against having uncaged dogs or other animals as passengers on private aircraft?
There is flight club at our field and this discussion came up.  A regulation cited would settle the matter.

In low gravity?

Interesting article: Flying with Your Furry Friend

CFR 91.13 Careless or reckless operation might apply under certain circumstances

FWIW, there's a difference between "uncaged" and "unrestrained". It's fairly common for to use a seat belt harness to limit a dog to the back seat but allow it some movement. I've never seen a specific regulation on this, but of course 91.13 is always there if the dog causes a problem. You might find the Pilots N Paws pilot guidelines useful.

Animals should be crated for the same reason passengers should be belted and all cargo properly stowed - in the event things go sideways, any loose item becomes a missile and can cause serious injury (of course, this assumes the crate is secured somehow; if it isn't, then it's no better than leaving the animal uncrated).

It appears that the answer is "there is no such regulation". For example, from AOPA's Flying with Family:

Airlines require that any animal on board be confined to an animal carrier at all times. Although there are no such requirements for general aviation aircraft, it is always better to err on the side of safety and keep them in a carrier.

Doesn't that lack of regulation compromise Part 91 section 107 that requires seat belts on all passengers?

@0tyranny0poverty: Section 107 refers to the use of safety belts by persons on board. I don't think animals qualify as persons for the purposes of the FAA regulations.

as in motor vehicles, I sense a disregard for animal passenger safety.

@0tyranny0poverty: I'm pretty sure the cages we get here are not safer than no cage; but then again I've seen some people ridiculously mishandle their dogs. In addition, the dog just doesn't understand why he needs to be strapped down.


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Why don't transponders send gps coordinates and other important info in addition to altitude and transponder code?
I heard that they were waiting for the patent holder's patent to expire, but just wanted to confirm.

Mode-S transponders with extended squitters (ADS-B) send this information, and is part of the Nexgen update.

\what patent and who is the holder?  GPS is only useful to increase accuracy.  Standard secondary RADAR knows the aircraft position already.  Are you asking about ADS-B or something else?  What  do you consider to be other important info?

Because many if not most transponders pre-date GPS?

@Simon I believe its this one https://www.google.com/patents/US5289183 .  Originally intended for motor vehicle traffic network, it has broad claims that would include said technology.  Google, Honeywell, Uber, Lyft, and many other companies were waiting for this and other patents to expire to totally revamp transportation networks while avoiding licensing fees.  Since this one was filed in 1992, it has already expired but I think there is another one they are waiting expiration on.  What other important data?  too numerous to list here.

Related

Basic transponder technology is old, predating GPS. Basic transponder operation (also called Mode A) only sends the programmed code, which can easily be represented as four octal digits. (In fact, before that, only two octal digits worth of data were programmed and sent.)
Later, a representation of the aircraft's (transponder's) altitude was encoded and sent along with the programmed code. This is Mode C.
As noted in the comments by Ron Beyer, the new transponder standard (the ADS-B Out technology) can send the GPS location information.
See also Why is the range of transponder digits 0 to 7 rather than 0 to 9?.


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Why was a Lockheed L-1011 chosen by Orbital ATK for its Pegasus launches?
Not sure whether this fits better here in Aviation, or would be better suited for Space, but since the question is about a terrestrial aircraft, I'll start it out here.
The topic of my question is why was the Lockheed L-1011 chosen by Orbital ATK as its aircraft launch platform for its Pegasus spacecraft launches?  On the surface, choosing an L-1011 seems odd because it's no longer being manufactured (not a big deal, probably), but also with so few airworthy L-1011 aircraft still in existence, it seems like an odd choice, being such an unusual aircraft from a maintenance and spare-parts standpoint.
Is there some performance reason that they chose to use an L-1011 that makes it a better aircraft for their launch purposes than other aircraft of similar size that have higher numbers of still-flying airframes?

One reason the L-1011 was chosen was that the keel beams on the L-1011 are spaced such that they could create an opening inside the aircraft for the verticle tailfin of the Pegasus when mated to the bottom of the aircraft and do so without jeopardizing the structural integrity of the airframe. This allowed them more clearance than other aircraft although the L-1011 still have to be jacked up to mate the Pegasus.
Second, while the L-1011 is no longer manufactured, there are enough of them still sitting around that getting parts was still an option, and in fact, sometimes entire aircraft were available for purchase.
Third, they were able to acquire their own L-1011 simulator from Delta and they operate it on a regular basis to maintain their flight currency. Since they own it they can make modifications to it to allow them to not only simulate their training environment but also their launch environment.
And lastly (although may not have been a consideration) some of the pilots of the Stargazer were Lockheed test pilots.
For more information, you should watch this short video:
NASA Edge Program - OrbitalATK ICON Program

It needed ground clearance for the rocket limiting the choice to the largest of the widebodies. At the time of selection (mid 1990s) the L1011 was already out of production and much cheaper to purchase than a 747 or MD11. Operating cost was immaterial due to infrequent use. You can see here that even with size, they still had to jack up the aircraft to get the rocket underneath.

Given the age of the L1011 launcher, an agreement was made in 2016 between Orbital and Stratolaunch to use the larger carrier aircraft for up to three rockets at a time. Few details were made public.

According to the source in ymb1's answer, it was 1992, so "early 1990s" rarther than "mid".

They're not the only ones turning to used aircraft to do this. Virgin Orbit is refurbishing a 747-400 from Virgin Airways. The benefits are

It's used. They can own it for far less than a new aircraft and retrofit as needed
Parts will be available from boneyards since similar aircraft are nearing retirement
It meets the need for hoisting heavier payloads. The maximum take-off weight of a L1011 is 510,000 pounds. That's a lot for an out-of-service aircraft.

Mighty Planes (Season 4, Episode 2) shows an animated view of the interior of the L-1011, with two keels spaced far enough apart for the Pegasus fin to insert into the fuselage.
That's the reason they give. They claim it is (or was) the only wide-body with two parallel keel beams.


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Military aircraft deliberate fuel dump capability?
I this question Why would a fighter drop fuel into a drone? it was essentially asked if the SU-27 has the capability to deliberately dump fuel in a controlled manner.  My question is if other current military aircraft (of any country) has the ability to do a controlled fuel dump, and if so, under what operational situations would this be considered a valid and useful military tactic?

The F1-11 could certainly dump fuel, and did so as an airshow trick when the pilot would ignite the dumped fuel with the afterburners. See https://m.youtube.com/watch?v=WpPEdOMSIgQ Fuel dumping can have uses for controlling landing weight. I can't think why else one would use it.

Highly related: this and other past answers to a related question -- https://aviation.stackexchange.com/a/47997/34686

Really the only time that’s used is just to reduce the weight of the aircraft in order to recover, i.e. reduce the weight to at or below the maximum landing weight of the airplane in order to land safely, just as is done on jetliners or other aircraft for normal or emergency operations.  Similar results can also be achieved by jettisoning ordnance from the aircraft, including external fuel tanks, but this procedure would be frowned upon during peacetime operations, and especially over populated areas. It’s simply easier to reduce weight by dumping excess fuel.
There is no other useful or military tactic associated with dumping fuel like that.  What you saw on that video was not some standard military tactic or interception procedure.  It was two Russian pilots hotdogging (and they have a VERY bad reputation for doing this during routine intercepts over international waters) and paid a high price for it.  I don’t know what the extent of damage to the SU-27 that collided with the drone was, but the pilot was probably darn lucky that he didn’t get killed in that circus stunt.

Well, the ONE useful use of fuel dumping with a military jet was the RAAF F-111C at the closing ceremonies of the Sydney Olympics. Not an actual "military" use, though. More an airshow thing.

I don’t know if you would call that a military procedure, per se. More like an airshow demonstration procedure.

Highly related: this and other past answers to a related question -- https://aviation.stackexchange.com/a/47997/34686


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Soviet (Eastern bloc) aircraft innovations?
From my Western perspective as a non-aviation person, it appears that most aircraft innovations throughout history (whether commercial or military) were pioneered by Western countries/corporations.  These innovations then were adopted (whether the information was obtained legally or by spying) by Eastern (aka Soviet) countries/manufacturers.
However, I fully admit my Western perspective on this topic, and am wondering if there have been significant aircraft innovations throughout history where the ideas were first formulated/developed in the East, and that information then adopted by Western countries/corporations later on?

Innovations developed by one side significantly before the other adopted them were not as common. With how long it takes to complete an aerospace program and the espionage capabilities of both sides, it was far more common for them to be developing similar technologies at approximately the same time. If the Soviets couldn't be first, they were sometimes the biggest or fastest instead. If there was a large gap, it was generally the Soviets that were behind, but they did succeed in bringing some technologies to production that never made it out of testing in the West. There are also some areas where the Soviets were the first and only to develop something uniquely useful to them.
Firsts (or close)

The Tupolev Tu-104 was the second jet airliner after the De Havilland Comet, and the only one flying following the grounding of the Comet and before the introduction of the 707.
The Tupolev Tu-144 was the first supersonic passenger airliner, beating the Concorde in both first flight and introduction by a few months. It was also both larger and faster than the Concorde, though not quite as many were produced and it was retired sooner.
The Antonov An-22 was the first wide-body transport aircraft and is still the largest turboprop aircraft, beating the A400M.
The Antonov An-70 was the first aircraft to fly powered only by propfans and is still the only production propfan aircraft.
The Buran spacecraft that the An-225 was built to carry was well behind the Space Shuttle, but was the first spacecraft to complete a mission autonomously, including landing, in 1988. Although the Space Shuttle got capability for autoland in the 1990s, it was never fully tested, and the next fully autonomous spaceplane flight including landing was not until 2010 with the X-37.
The Sukhoi Su-30MKI, developed by Sukhoi in Russia and built under license in India, had thrust vectoring in both pitch and yaw, entering service in 2002. Other than vertical takeoff use in the Harrier, the West did not have a thrust vectoring fighter in service until the F-22 in 2005. The F-22 only has thrust vectoring for pitch.

Largest/Fastest

The MiG-25 and MiG-31 are still the fastest fighter aircraft in the world.
The Ilyushin Il-62 was the largest jet airliner when it entered service in 1963.
The Tupolev Tu-114 was the largest and fastest passenger airplane on its introduction in 1961, and is still the fastest propeller-driven aircraft.
Though developed after the C-5, the An-124 is larger, making it the largest aircraft ever mass produced.
The Antonov An-225 was the largest aircraft in the world and set 240 records, including heaviest single cargo item, heaviest payload, and longest cargo. Although the Stratolaunch aircraft has a longer wingspan, the An-225 was still longer and had a heavier max takeoff weight and payload capacity.
The Mil Mi-26 is the largest helicopter to be serially produced.
The Tupolev Tu-160 was developed in response to the B-1, and entered service a year later. It is the largest and heaviest Mach 2+ military aircraft ever built. It is still the largest and heaviest combat aircraft, the fastest bomber in use, and the heaviest variable-sweep wing airplane ever flown. Only the experimental XB-70 was longer and faster.

Unique Aircraft

The Be-10 was a jet-powered flying boat that only lagged the Martin P6M by a year, and entered (limited) service while the P6M was canceled. The newer Be-200 appears to be the only large jet-powered flying boat currently in production and service.
The An-72 was developed well after the AMST program (which eventually led to the C-17) but is unique in being a production aircraft using the Coandă effect.
The Soviets were pioneers in Ground Effect Vehicles. Though service was limited, these include the massive KM known as the Caspian Sea Monster, with a maximum takeoff weight of almost 1.2 million pounds (544,000 kg). The KM was the largest airplane in the world during its time, and was only surpassed by the An-225.
The concept of a coaxial rotor helicopter was actually a originated in Russia by Mikhail Lomonosov in 1754. In modern times, Kamov is known for their coaxial rotor helicopters, with their first mass-production version being the Ka-15 in 1955. The Ka-50 and Ka-52 from the 80s and 90s respectively are modern attack helicopters. These appear to still be the only large mass-produced coaxial helicopters.
The Mil Mi-24 is still unique in operating as a troop transport and attack helicopter at the same time.

The second jet airliner to fly after the Comet was the Canadian Avro Jetliner, which flew a few weeks after the Comet and would've been first if not for a last minute technical glitch. It was a sensation when it went on a US sales tour.

First off-boresight missiles was also Soviet. The Americans was especially surprised that the Su27 could fire a missile at a target behind it (not directly behind, more like 130 degrees or so)

Also, let's not forget that while most of the development of delta wing aircraft in the West is attributed to Lippisch, in USSR Kalinin was also developing delta wing designs contemporary with Lippisch

Re the Tupolev-144, it was an attempt at a direct clone of the Concorde. Nothing innovative about it. More specifically, it lacked Concorde's supercruise development, so flying it commercially was impossible; and it lacked all the control technology that went into Concorde, so it crashed at the Paris airshow and remained untrustworthy. I'm not sure how it belongs on the list.

About Tu-104 - by some it was considered the deadliest aircraft, and while Comet cancelled its flights to improve, soviets cared less and only cancelled it after it was (ab)used for more than 20 years and went out of commercial service in 1979. It onlyness was not technical, if british didn't care, they would use the Comet and tu-104 would not be the only. An-70 - despite tears in my eyes, I would not agree with you that this is a production aircraft. But thanks for the awesome answer!

WRT the SU30, I don't know how you can blithely discount the Harrier - where the thrust-vectoring was widely touted as a useful combat feature, even gaining a specific name: "Viffing" .

I think the Antonov AN-2 is the largest passenger capacity, single-engined bi-plane ever built?

Yes actually there were some innovative aircraft developed in the East. The Soviets built the ultra long range ANT-25 in the 30s, which flew across the North Pole to the USA non-stop.
Check out this youtube channel, by the son of a Soviet Air Force fighter pilot on stories of Soviet aviation. Fascinating and amusing. A real gem.

Unfortunately, the channel's author sacrifices faithfulness for drama, giving a skewed perspective in many cases.

The next information might be considered:

Year: 1867

Name: Телешов, Николай Афанасьевич
Pulse jet with fuel injection
Jet airliner (120 passengers)
Delta wing *same year as Butler and Edwards
Tailless aircraft *same year as Butler and Edwards
Pic: https://commons.wikimedia.org/wiki/File:Improved_System_of_Aeronautics_of_N_Teleshov_(project)_1867.jpg

Year: 1933

(Flying prototype 1937)
Supersonic delta wing
Name: Александр Сергеевич Москалев Alexandr Sergeievich Moskalev
Pic: https://images.techinsider.ru/upload/img_cache/c05/c05931b29b76cc2556ffe0472bcf7c7b_cropped_666x260.webp

Year: 1911

Name: Boris N Yuriev
Swashplate
https://en.wikipedia.org/wiki/Swashplate_(aeronautics)

Year: 1909

Name: N V Gerasimov
Turbojet engine
Pic:

Year: 1914

Name: М. Н. Никольской  M N Nikolskoi
Turboprop engine
Pic: https://ic.pics.livejournal.com/raigap/40496274/4062394/4062394_original.jpg

On race of who made the invention, invention is usually made in an improvement process as a whirl, where some time one person is higher, some time another, naming one person an inventor would cause the other people work to be attributed to him/her. A point would be even and unbiased if people had been granted according to their contribution. At the same time the system of attributing the invention to a single (or a single entity) inventor makes possible to hide, transfer, misattribute, and practically sometimes is grounded on misattribution because usually there are certain contributions of other people. Then, it makes possibility to fix invention on certain points of the process where certain people are ahead trying to hide same points when other people are ahead, not including theoretical researches being more important. It highly depends on capabilities to reach a Patent office, profitability of invention business in a country, possibility to get required research and production equipment, even the mood and social realm, for example in socialism to use invention for personal profit is not very much respected, but to share with people for common profit is respected; therefore, who has invented may share new method or apparatus openly. There were author certificates, they were not of huge profit, more as points of recognition. The invention may be then reused and improved.

I made some formatting changes to make it come out the way I think you wanted it. I do note, though, that point 1 claims a jet airliner in 1867! I'm sure that's a typo for 1967. You can [edit] that yourself to clarify. The wall of text after that, though, seems entirely off-topic as a discussion/rant about attribution of credit for an invention. If I'm reading that correctly, it really doesn't have anything to do with the question or answer and can easily be deleted without losing anything.

Also, if you'll take the [tour] and spend a few moments reading up on how to write a good answer, you can [edit] this to better fit the format here. "Consider this information" isn't really the type of answer we're looking for.


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How are wing tanks sealed around the internal wing structure?
I can easily grasp the idea of tanks of fuel inside the fuselage of an aircraft, and the ease of sealing such tanks in a relatively standard shape.  However, I'm having a hard time understanding how wing tanks could be fit around the internal structure of a wing, as I envision the inside of a wing (especially nearer to the fuselage) to be a honeycomb of structural pieces that would be very difficult to seal around or find any large volumes of contiguous space for fitting tanks.  Is the wing structure itself the fuel tank, or are there separate fuel tank bladders that are somehow fit into the wing voids?
For my question, I am not concerned about military fuel tanks which might have special materials in the walls which could seal off a leak due to combat damage, but rather just non-military aircraft.

https://www.youtube.com/watch?v=giEMzfmQoqs

The gist is that there isn't a tank in the wing, the wing itself is the tank. All the internal structure is simply immersed in the fuel.

The tanks are generally sealed with some kind of putty/resin/epoxy like material. Keep in mind that only the joints between exterior panels need to be sealed. On many aircraft this is done through inspection panels. The material is, in a manner of speaking painted/applied.
Here is an example from a Mooney, which are pretty infamous for having in wing tanks

(source)
Tanks on larger aircraft are not all that different, much like this one off a 747

(source)
its worth noting that tanks don't need to be continuously open, they can have structures with in them as long as the fuel is free to flow around. Large and small tanks alike may very well have structural elements inside with flow holes drilled to allow fuel to move around. These elements also help reduce the effects of large quantities of fuel sloshing around as the aircraft changes attitude.

Indeed, continuously open tanks are often bad -- the fuel sloshes around, which can be a bad thing for a vehicle that's so sensitive to the position of its centre of gravity. I believe road tanker trailers usually have baffles installed to prevent partial loads surging forwards under braking.

The wing of large airliners gets its strength ffrom the wing box structure: the skin on top and bottom of the wing take compressiona nd tension loads, two spars mainly keep them apart. Stringers are attached to the skin to keep them in shape.

That means that the wing has a hollow inside, which can be used as a fuel tank. The wing box is the tank. It is sealed at the edges by resin; some anti-slosh structures are put in place as required.

The existing wing structure of front and rear spars and upper and lower wing skins act as an integral wing fuel tank. When the wing is assembled sealant is applied between all parts to make the wing water-tight.
While fuselages are primed with green primer paint, integral wing tanks are primed with special yellow primer which is made to be a barrier against the fuel.
An airliner wing will have a "dry bay" just over the engine for safety in the event the engine were to explode and throw turbine blades into it. On a 777 the Dry bay area is blocked out by a composite piece that is secured and sealed in place.
Each wing will usually have one dividing wall in it in the vicinity of the engine pylon (everything inboard from that point is considered the center wing tank, including the center wing section/tank).
Airliners with 4 engines will have each wing divided into at least 2 sections (one to feed each engine).
Perfectly sealing the inside of the wing is very important.
There are lots of QA inspections and a final test.

Composite aircraft also have integral tanks. Even gliders have them, only for water ballast. A composite fabric will never be completely tight, so the tank walls need a waterproof coating. This also helps to reduce water absorption by the epoxy matrix - wet epoxy has lower strength.
Below is a photo from the wing assembly of the composite flying wing SB-13. This is the moment when the mold with the lower left wing shell is placed on the opposite half with the upper left wing shell. The light grey area is the water tank coating, and it contains two ribs mounted in lateral direction to reduce water sloshing. In a flying wing with its limited pitch control, longitudinal sloshing is quite undesirable.
The coating is simple swimming pool paint. After the wing was bonded together, more paint was poured into the tank and the wing was moved around to ensure that the sloshing paint covers all remaining surfaces, especially those that had to be left unpainted to ensure proper bonding.

Note the pushrods: There are four (two for the elevons, one for the winglet rudder, one for the speed brakes), three of which enter the wing at the root ahead of the spar. Rocker levers transfer the motion to the outer wing pushrods which are behind the spar. The spar itself has three degrees less sweep than the wing to improve aeroelastic damping.


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Adjustment for non-balanced passenger loads?
It is well established (How Centre of Gravity (CG) is adjusted? and elsewhere) that adjustments can and need to be made to insure that airplane loading maintains a suitable center-of-gravity for the aircraft fore/aft.  However, these questions and answers appear to deal only with fore/aft adjustments.  Does a plane such as the MD-88 which has unequal seating (3 seats on the port (left) side of the aisle and 2 on the starboard (right)) have much of an issue with port/starboard balance, and if so, is there standard way of dealing with more passenger weight on the port side of center-line?
I would assume this could be handled with unequal fuel tank loading in each wing, or air surface adjustments, but am curious if in practice this is an issue or not.  Or is there anything built into the design of the aircraft to handle this expected unequal passenger loading?

It's not a problem for pax aircraft. However, large cargo aircraft typically have a max lateral imbalance moment. As I remember, it's 10,000,000 in-lb for a 747-100/200. if you want to see an example, go to 747.terryliittschwager.com, dismiss the opening modal window (click ok), scroll to the bottom of the page and click the button to the right of item 6. The resulting test load, obtained by loading only one side, will come up and will violate that limit. You can scroll down the page to the LATERAL LOADING IMBALANCE envelope to see the violation.

Interesting.  We never calculated lateral CG in the C-130.

You'd be amazed how little the flying characteristics of a radio-controlled model airplane (in at least once case) were altered by adding a significant weight to one wingtip only.  Of course, that might have been due to the fact that the model in question had lots of dihedral, so increasing the wing loading of one tip to make it "want" to fly faster created a yawed/slipping condition that contributed a roll torque component AWAY from the weight, partially offsetting the "direct" roll torque component caused by the weight.

Asymmetrical lateral loads within the fuselage are not far enough away from the longitudinal axis to generate any significant moment arm.  It is an issue, but not one that is planned around or proactively compensated for.  Any imbalance in flight can easily be overcome with a little bit of aileron trim.

On the MD11F we needed to calculate the lateral imbalance and there would be a Max Take-off weight penalty but the penalty was capped at 15,000kgs IIRC (around 17years ago!).
Reason we were told was to reduce side stress on the landing gears.
Anilv

Passenger airliners do have lateral C of G limits in addition to longitudinal ones.  Nobody ever actually calculates the limits but it's usually what's behind the lateral fuel imbalance limits, taking into account normal left/right passenger distribution.  Airplanes with an offset center aisle will have only a minor lateral imbalance compared to symmetrical seating, although it would be interesting to see if the MD-88 has slightly asymmetrical fuel imbalance limits to compensate.  In any case with, normal passenger lateral distribution and balanced fuel, there isn't normally an issue on any airliner, offset aisle or not.
Lateral CG limits have an influence on required trim authority.  For FAR 25 certification, the airplane is only required to be able to be trimmed hands off in roll with lateral CG at the maximum offset throughout the normal speed range (approach thru Vmo).  Most airliners have way more than enough trim authority to meet that requirement.
On the Regional Jet, pilots would get way too fussy and frequently snag cruise lateral trim requirements (caused by aerodynamic asymmetries of an otherwise balanced a/c) of more than about 13% (basically if the trim input in flight was enough to be outside the takeoff range after landing, they would snag it) although per FAR 25, way more trim could be needed and still meet cert requirements in the RJ's (or most other a/c's case).

The difference would only be one seat slightly to the left (or right) and the moment (distance) is pretty insignificant.

Yes almost certainly small enough to be "lost in the noise" of other factors.


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Bright exhaust in afterburner vs no visible (bright) exhaust when not in afterburner?
When a jet engine has its afterburner engaged, a bunch of fuel is dumped into the back of the engine for additional thrust.  This burning fuel causes the exhaust and inside the engine to glow brightly, which is quite visible even to the casual observer.  However, when the afterburner is not engaged, there is no visible light at all that I've seen coming from the engine's exhaust.  I would think that the fuel burning process of a normal jet would be visible out the back as well, just not as noticeable as afterburner exhaust, but that doesn't seem to be the case.
Is there visible light from the exhaust of a non-afterburner jet and I'm just not seeing it, or is the burning fuel inside the engine so much that it just doesn't get out.

It's because on a jet engine the flame in the burner can is carefully controlled and contained by airflow that is guided in from the sides to keep the flame in the center of the burner can so it doesn't touch metal (only maybe a 3rd to half of the airflow out of the compressor gets burned; the rest is for temperature control - which is why there is enough oxygen in the air leaving the turbine to support reheat).  The flame is supposed to be out before the gasses have left the burner can or else the turbine will overheat. The turbine itself is getting burned air that has been mixed with un-burned air to cool it off.
On most engines, if you see a light in the tailpipe of an engine not in reheat, it means there is a flame aft of the burner can in the turbine zone, which is very very bad, except when initially starting and some is briefly visible after lightup.
On some engines, if there is a direct visual path up the tail pipe, through the turbine and stator blades, into the center of the burner can, you may be able to make out a bit of bluish light (should be bluish; yellow light means too rich and the yellow is un-burned carbon fluorescing, like any yellow flame).


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Engines more powerful than the brakes?
This might be more of an anecdotal question, but are there any aircraft where under full throttle (with afterburner in worst-case) where the wheels wouldn't provide enough friction against the runway to keep the aircraft from starting to roll (and skidding the locked-up tires)?  Obviously if the runway was iced it would make a difference in friction; I'm more wondering about in normal runway temperatures where it's just rubber on concrete.

It highly depends on the weight of the airplane, because it's usually the friction between tire and runway that limits braking force, not the friction between brake rotor and pads. Those airplanes are very common, basically almost all jet fighters whose weight is not much greater than thrust and simply there's not enough gravity to generate enough friction to counter act the thrust. This is why ski-jump aircraft carriers uses a wheel choke to stop the fighter from rolling instead of relying on brakes. Field engine test is also a interesting problem for high power jet fighters.

Possible duplicate of Can the wheel brakes hold an airliner in place if its engines are at full thrust?

Also this one

I don't think this is an exact duplicate, that was asking about airliners in particular. I do think this is too broad however.

There's plenty of good information on the other linked questions, but I also don't believe this is a duplicate.  Unlike @GdD, I think this question is fine as-is.

Many small 4 to 6 seats propeller airplanes can overcome their brake/wheel holding capability, on concrete and ashpalt.  My Cessna Cardinal is 180HP, I do engine pre-takeoff runup checks at 1700-1800 RPM. Going to 2600, the plane will start moving.  Many other planes of similar size are 300 HP, and they definitely won't hold. We only have two 5" or 6" disc brakes, no power assist, pushing the pedal tops with our toes. Or a hand-pull parking brake.


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How does a plane's weather radar ignore returns from other weather radars?
In busy and congested airplane areas (around large airports, for example), there could be dozens of commercial aircraft, all with their own weather radar transmitters/receivers actively transmitting and receiving radar signals.  How are the radar receivers able to discern between their own radar's returns from those of other aircraft?  I can't imagine them to all have different TX frequencies to prevent interference, but not sure how else the receivers could be set to reject other aircraft's radar transmissions.

Does this answer your question? What is garbling in the context of radar?

Not a dupe at all. This question is about the radar transmissions themselves; the suggested question on garbling is about transponder replies.

Edited to hopefully clear up some of the confusion (although I find the question entirely clear - and a good one). As the OP notes in a comment below, this is NOT about ATC radar nor transponders whatsoever. It's all about why one aircraft's weather radar doesn't interfere with another aircraft's weather radar.

My complete guess, without knowing anything about the situation, is that the radar in each plane may not be using the exact same frequency radio waves. It might be a set variation determined at the factory or they might be able to "listen" before a scan and automatically select a frequency that isn't in use. If I were designing the system I would attempt to create such a feature.

"Radar to radar interference" / "Mutual radar interference" is an ongoing research topic, though much of the current research (based on my cursory Googling) seems focused on interference between radars on self-driving cars.  That leads me to believe a certain degree of radar-to-radar interference is currently just tolerated.
The link shared by randomhead gives us some insight into how maritime radars mitigate mutual interference, both directly and indirectly.  The same techniques should be applicable to aircraft weather radars, which tend to also be X-Band and also be pulsing radars.
Directly

The interference rejection capability of the radar essentially relies on timing differences between the radars.  A pulse radar sends out many pulses, separated by around 1 millisecond.  Microsecond-resolution timing between the transmission of the pulse and the receipt of its echo is used to determine range to a target.
Interfering radar pulses will arrive somewhat randomly on that microsecond timescale, but actual target echoes (e.g. from weather) will be correlated across multiple pulses.  The radar can be made to only acknowledge a return as real if enough echoes arrive.  Related topics here seem like "m-out-of-n" detection, "binary integration", "coincidence detection", "dual threshold detection", and "double threshold detection".
Activating the "interference rejection" mode on a radar (or having it always on, which I suspect is the case on many aviation weather radars) will cause a radar to reject certain weak real returns (more false negatives).  Luckily, clouds full of precipitation tend to return radar fairly well.

Indirectly

A different section of the same link gives instructions for tuning radar.  This implies that there is room in the band for more than one transmitter to be operating simultaneously, though it may not be organized formally into channels.  This is reinforced later in the description of the Search and Rescue Transponder (SART) scanning the radar band for pulses to reply to, which wouldn't be necessary if they all operated on the same frequency.
So, automatically or manually, weather radars should also be able to deconflict by frequency separation.  This will, of course, run into limitations as the number of transmitters grows, but at least it reduces the amount of work the Interference Rejection mode has to do.

If the radar can change properties of its pulse, such as the pulse length or frequency modulation, it can potentially use those properties to distinguish between its pulses and pulses from other transmitters.  The link doesn't really support that being used to reduce interference in maritime navigation radar, though, and I kind of doubt it's used for such in aviation weather radar either.  I think I've heard of schemes like that being used for more warfare-oriented radars but that's even further outside my own expertise.

I doubt this answer is good, per se, but I hope it can be a nucleation point for many edits or attract the attention/ire of someone who knows better.

I agree, the current generation of aviation weather radars are extremely sophisticated. The only people that would know are the designers and coders and that knowledge would likely be intellectual property and possibly sensitive export controlled technology.

@Jabirhee uhhh there's tons of research papers out there discussing methods for interference rejections, so...I dunno about the export control status.  I've just had difficulty finding aviation-weather-radar-specific sources among all the other related radar topics.

Yes, there are plenty of academic papers and textbooks on radar systems. I know of 2 companies that successfully manufacture modern weather radar systems for transport aircraft. They both probably have government contracts with the US government too. Anyone doing business with them will be subject to a non-disclosure agreement and the company will likely have a policy for adhering to ITAR regulations. A few of the people that work there would be able to accurately describe what factors are relevant and what methods are effective for achieving a good result.


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Should I put yesterday's date for destination date/time on a flight plan if the flight is to go east bound across Zulu +-12 time zone?
The international date line runs across the middle of Pacific Ocean opposite (12 hour ahead or before Greenwich mean time (zulu)) Zulu time.  It is the boundary where 24 hours elapses and the date changes.  I am trying to clear the fog in my mind how pilots account for the date on their flight plan when the flights cross Zulu+-12.

Related (not at all a duplicate): How should night time be determined and logged in a fast westbound plane?

When you file a flight plan, you don't enter an arrival date or time. You just enter proposed UTC departure time and estimated length of time enroute. For aircraft or pilot logbooks we only use UTC date and time for departure, and UTC date and time for arrival. The local arrival date or time does not matter. The international date line has no bearing on UTC date or time.


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Are artificial magnetic fields used or proposed to be used to shield high altitude pilots and astronauts from charged, high energy radiation?
If not for the earth's magnetic field our atmosphere would be bombarded by high energy plasma (ionized gas) from the sun and other space sources.  At very high altitudes and orbital altitudes this protection is less and when space travel takes astronauts out of range of earth's magnetic field there is no protection.
Does the International Space Station or other craft have an artificial magnetic field to protect its astronauts?  If not are there plans for implementation?

You may have better luck with this question on Space.SE or even Physics.SE, since you are asking about a theoretical technology. I'm sure that somebody has considered it, but the actual implementation I think is outside the scope of this site.

The ISS is not shielded because it is below (300/400 km altitude) the Van Allen belts. A shield would be needed if you go out of the magnetosphere, or more accurately, at some altitude before the magnetopause. The latter is not a sphere, but on the Sun side it's about 10 Earth radii, more than the geostationary orbit. If needed, it would require only about 2 or 3 kW to create a protective magnetic field around a spacecraft (Earth field is only 50,000 nT). See this question on Space.SE.

This won't work.
What to shield
Most of the cosmic radiation has quite low energies and can easily be shielded by the hull of an aircraft, spaceship or spacesuit. This would also be shielded by the atmosphere, but it would also burn/blow it away over time due to the intensity of the radiation. For luck, the magnetic field of the earth shields us from this radiation before it reaches the atmosphere.
And then there is the nasty stuff. Particles with energies which can easily punch through several centimeters of iron, lead or whatever. This stuff can not really be shielded by the magnetic field of the earth, nor could it be by artificial fields. Even worse, when this stuff hits a nucleus in the hull of a spaceship, it would smash it into many pieces, which will then fly along the direction of the original particle. Yes, this means radiation can be even higher behind a too thin shield! And since this happens in the hull or in the spaceship, one can't shield that by fields outside the ship.
In fact, most of the radiation in aviation is not made of the primary particles from space, but of secondary particles created in collisions between the primary particles and atoms of the atmosphere.
Field strength
The most important factor of field strength of a magnetic dipole is
$$B(r) \sim m/r^3$$
(Yes, to the power of three)
$m$ is the magnetic dipole strength, which for a simple conductor loop is given by current times area enclosed by the conductor.
So, if we build a coil of several thousand windings, resulting in a total current of several thousands of amperes, and an area of some ten squaremeters, we end up with an $m$ of several 10000Am². In contrast, earths magnetic field has about $8\cdot10^{22}$Am², which is a totally different order of magnitude.
Earths field strength might not be high - only about 40µT at the surface, but it reaches far, far into space. So, the time / distance the field acts on a particle is quite long, an can deflect it easily. In contrast, a human-made field will decrease to near zero within just a very few meters, and that's not enough.


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Is there any other category of aircraft in the FAA regulations besides 'Ultralight' that does not require pilot licensure?
I am asking to clear up contention on my related question that was put 'on hold' by the moderators.  To my knowledge, there is no other category of aircraft besides 'Ultralight' as defined in CFR 14 part 103, that doesn't require any kind of pilot's license.  The 'experimental' category requires a recreational pilot license.
The problem with the 'Ultralight' category is that in practice it ends up being discriminatory against heavier potential users.

As an aside, the community puts questions on hold.  Rarely do moderators intervene.  Your question was closed by people voting to close it.

You clearly want to fly,  but seem opposed to getting a license.  Why? Do you drive a car without a license too?  Just go get licensed; it will make you a better pilot,  and you will learn a lot.

@abelenky I am a pilot.  This is not about my personal flight ambitions.  I am trying to see under which regulatory framework the self-piloted Personal Aerial Transport Vehicle (PATV) would fit.  envision a Jetsons type Local Aerial Personal Transportation Network (LAPTN) where you board the PATV, set your desired destination and the PATV would automatically fly you to your destination in coordination with the LAPTN.  don't need drivers license for self-driving cars, don't need pilots license for self-piloted PATV

"don't need drivers license for self-driving cars". That's new to me, as the driver so far was not relieved from their total responsibility to drive the vehicle, the software being only an assistance to the driver, from the standpoint of the law. Nobody will pay fines or go to the court, but the driver.

@mins "driver so far was not relieved" yet.  Just a matter of time.  As the the trends increase our visibility going forward in the time domain, the PATV in LAPTN scenario described will become real and the regs must adapt.  There is no debate on "if" this will happen, just "when"

"There is no debate on "if" this will happen". In your scenario the damages to others will be paid by the manufacturer. This means the manufacturer will have their insurance company pay for them. Then the insurance company will sell their contract to the manufacturer at a price equivalent to the sum of all the previous driver premiums (same risk, same price). Indeed, no manufacturer will do that because it's absurd, and the driver will still be liable, and will need to know the highway code.

@mins Putting aside the matter of who takes the risks, who benefits, who pays, public vs private, etc.  Don't you see this Jetsons type of PATV in LAPTN happening in the future?

Yes, there is at least one. This probably was not what you had in mind, but the FAA has been very explicit about the following, for a variety of reasons.
Unmanned aircraft are explicitly regulated as aircraft. However, certain model aircraft require no certificate if operated under the provisions of §101. This is in contrast to all other unmanned aircraft which do require some sort of certificate or exemption, Small Unmanned Aircraft Systems regulated under §107 for example.
The following definition is from 14 CFR 1.1:

Aircraft means a device that is used or intended to be used for flight in the air.

The following is excerpted from the FAA's FAQ page on Unmanned Aircraft Systems:

What is an unmanned aircraft system (UAS)?
  An unmanned aircraft system is an unmanned aircraft and the equipment necessary for the safe and efficient operation of that aircraft. An unmanned aircraft is a component of a UAS. It is defined by statute as an aircraft that is operated without the possibility of direct human intervention from within or on the aircraft (Public Law 112-95, Section 331(8)).


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Can glide ratio be increased with bi-wing configuration?
We all know that increasing the wingspan of an aircraft tends to increase the glide ratio.  Instead of increasing the wingspan, could an extra wing of the same size or less as in a bi-wing configuration also increase the glide ratio?  Which bi-wing configuration would be most ideal for this purpose?

The reason L/D is increased in wings with large aspect ratio is because the % of wing subject to wingtip vortexes is smaller and less lift-induced drag is generated.

@mins, the % of wing subject to wingtip vortices is all of it, always. Wider span does mean less induced drag, but the reason is that the wider downwash does not has to be as strong (and therefore the vortices are not as strong, because the vortices are just the shear between the downwash and the still air outside the span).

@JanHudec: My comment is based on two Nasa statements: 1/ "The vortices produce a down wash of air behind the wing which is very strong near the wing tips and decreases toward the wing root.", 2/ "Induced drag is a three dimensional effect related to the wing tips. The longer the wing, the farther the tips are from the main portion of the wing, and the lower the induced drag".

@mins, it probably makes sense in the context of the convoluted explanation (based on potential flow theory?) they use, but it is seriously confusing. Fortunately there is no need to involve vortices in explaining induced drag at all—the energy argument is most elementary physics (just laws of motion and conservation of energy).

Glide ratio is determined by L/D. If we can increase lift without increasing drag, or decrease drag without decreasing lift, we have a better glide ratio.
Increasing the wing span (for a given wing area => reduce the chord) helps: the longer wing span spreads out the lift creation over a longer distance, thereby decreasing induced drag. Keeping the flow laminar for as long as possible also helps.
Your question is about adding a second wing to an airplane. The problem with biplanes is that they were mainly constructed decades ago, and we associate them with older construction methods and mainly lots of drag, such as addressed in this question. It seems that the classical biplane has no aerodynamic advantages, and always has a lower L/D ratio than a comparable mono wing.
However there are now Computed Fluid Dynamics. There has been work done on biplane configuration with low drag in recent years - many are behind a pay wall, this one is not. Their work found two configurations with high L/D ratios:

Upper wing AoA = 13º
Upper wing forward sweep = 30º
Lower wing AoA = -2.8º
Lower wing backward sweep = 3.5º
Wing profile of both wings = NACA 4412
Both wings 6 ft span and 6 inch chord
Computed L/D = 32.3

The other configuration they found with a high L/D was a canard configuration: one wing in front of the other. If you insist on using two wings, this may be your best bet: one wing mounted in front of the other, in such a way that the back wing is out of the way of the wake of the front wing, or mounted at the optimum AoA for the disturbed flow. Their canard configuration used two different wings, resulting in an L/D of 35.8:

Note that none of the configurations included a fuselage of any kind, so their CFD work would have to be repeated with the fuselage and with interference computations. Fortunately computing power has increased dramatically in recent years.

Second to last bullet: "Both wings 6 ft soon and 6 inch chord". "6 ft soon"? Was that supposed to be "6 ft long"?

Fixed it, thx..

Instead of increasing the wingspan, could an extra wing of the same size or less as in a bi-wing configuration also increase the glide ratio?

To create lift (over finite span), which is upward force, the wing apply downward force to the air by principle of action and reaction and since the air is free to move, it will accelerate downward. This will increase its energy, therefore the wing must do some work on it and this work manifests as induced drag.
Now because kinetic energy is proportional to mass and square of velocity, while momentum is only proportional to mass and velocity, it is more efficient to accelerate more air to lower speed than less air to higher speed.
At given flight speed, more air can be affected by increasing the wing span, or by having two wings far enough to affect different air. Since the wing affects air to height comparable with the span, the wings would have to be quite high above each other for the construction to be efficient—but such construction would not be efficient mechanically, since it would need very high pylons above and possibly below. Increasing the span is easier.


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Is the nose cone of the MiG-21 adjustable in-flight?
In some of the photos I saw of the MiG-21, the nose cone was extended and in others it was shortened. So, is the nose cone of the MiG-21 adjustable in-flight to allow for increased/decreased air flow?
I noticed on a video yesterday from another question regarding the nose cone of the MiG that the SR-71's engine cones are adjustable, so that led me to believe the MiG's might be as well, though nobody mentioned it specifically in that particular question.

Welcome to Aviation.se!

Welcome to Aviation.se. On Stack Exchange, we prefer short and precise questions. I have removed some personal details and "thank you" sentences that are unrelated to the question itself.


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What is the temperature at the center of a gas turbine disc?
I realize that it varies with the temperature at the inlet of the turbine, materials, dimensions, etc. But I would be interested in knowing an orientative value. For example, for a turbine which has at the exit of the combustion chamber a temperature of 1300 K. For the first turbine stage, around what temperature will the shaft/ center of the disc be? We have no cooling system.


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Why would a NOTAM outage cause a nationwide ground stop?
From the FAA this morning

The FAA is working to restore its Notice to Air Missions System. We are performing final validation checks and reloading the system now.
Operations across the National Airspace System are affected.

This apparently caused a complete ground stop for the whole US. Why?

NOTAMS contain information about potential hazards and other mission-critical information that is short-lived (so not worth printing on charts) or otherwise breaking news kind of stuff.
Without that information, pilots will be unaware of dangers that may be involved in their flight.
VFR traffic was exempt from the stop, presumably because VFR flying relies far more on pilots' own ability/requirement to detect obstacles/trouble, and GA (which operate under looser regulations and may choose to accept more risk than airlines are allowed to accept on behalf of their passengers) were among the first to be additionally exempted prior to the ground stop itself being lifted.
But airlines are heavily regulated and aren't allowed to depart without reviewing the NOTAMS relevant to their flight path and if the NOTAM system is offline they're unable to meet that regulatory requirement.

@757toga I'll edit. I was listening to KBOS_GND/DEL when it dropped which is how I know VFR traffic was exempt from the ground stop.

This answer is largely correct with the exception of the presumption about VFR.  Whatever the reason for the VFR exemption, it wouldn't be for the reason stated.  NOTAMs often contain information vital to the safe conduct of VFR flights, cf https://www.notaminfo.com/latest?country=UK+Channel%20Isles

@Dave Grimlin That's true. Ask any VFR pilot that accidentally flew into a Presidential TFR.

I think VFR traffic was allowed due to the need for life-safety flights, e.g. medevac, SAR, firefighting, to continue.

@user71659 ISTR they also explicitly exempted Medivac flights and the like separately, but it's now been 12 hours or so since I heard it so I may be mistaken on that.

@user71659: it was originally a complete 100% everybody GS, then they exempted medevac and military, then they exempted VFR, then they exempted IFR general aviation, then they exempted flights to ATL and EWR, then they also exempted flights to IAD, then they lifted the stop entirely.

I think a better question is:  Why, if this system is so critical, does it not have some sort of redundant backup that would immediately kick in to avoid a complete shutdown like this?

@DarrelHoffman AIUI, they did have a backup system... but that backup system had the same corrupted file so it also failed.


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Is AMDAR a required system on aircraft?
I was intrigued by the assertion that COVID-19 depressing commercial aviation has lead to lower quality weather forecasting

The aircraft observations are a key piece in the jigsaw of national and global weather data that is fed into computer models through a process called data assimilation. Multiple studies have found that aircraft are among the most important data sources for reducing the error in forecast models.

After some poking around, I found out the system is called AMDAR

The AMDAR system predominantly utilises existing aircraft onboard sensors, computers and communications systems to collect, process, format and transmit meteorological data to ground stations via satellite or radio links. Once on the ground, the data is relayed to National Meteorological and Hydrological Services (NMHS), where it is processed, quality controlled and transmitted on the WMO Global Telecommunications System (GTS).

Is this system required by aviation authorities anywhere? Or is there merely some incentive system to encourage participation?

Airlines directly benefit from participating by getting better weather forecasts back.

AMDAR (Aircraft Meteorological DAta Relay) is a program established by the World Meteorological Organisation to gather weather data from around the world. It's run through a number of local and regional AMDAR organisations who negotiate with partner airlines arrangements to use existing aircraft sensors to gather and report weather data on each flight.
The gathered data is relayed by satellite or radio to ground stations and then forwarded on for processing and distribution.
(I've paraphrased from this source)
So, there is no specific AMDAR equipment. The AMDAR system is implemented by arrangement with partner airlines, and may be installed on some or all of the airline's aircraft that already carry suitable sensors.
There is no mention of a requirement that an airline partner with a regional AMDAR organisation, and thus no requirement for their aircraft to carry the system.
It's not clear from the pages at the WMO what the nature of the collaboration between the local AMDAR organisation and the airline is, so there may be some payment to the airline, or there may be some benefit in kind: free or reduced cost access to meteorological reports, perhaps.

Short answer: No. It depends on the type certification of the aircraft. For example, helicopters don't even have radars! Also, many old planes (e.g., DC-3, DC-8, MD-80) aren't equipped with AMDAR. So no, not ALL planes have to be equipped with AMDAR, but AMDAR is quite useful.
Usually the rule on AMDAR is the higher and faster your aircraft goes, the more an aircraft weather monitoring system is required. F.e, fighter jets and modern long range jets have to be equipped with some kind of weather monitoring system.  Basically, sometimes weather radars in general are required.

If you're going to contribute here, please try to include relevant sources. Much of what you have written here appears to be your personal opinion, and of rather doubtful quality. For example, AMDAR is not a company, although you seem to think it is.

Please do contribute here, just make sure that you're quoting reputable sources to back up your assertions. Taking the [tour] and browsing through the [help] (particularly the sections about answering), will help make your questions and answers better.

@CatchAsCatchCan: I'm sorry, I'll edit that out. But I'm pretty sure I read somewhere that AMDAR was a company. Personally, I doubted it, but I decided to put on here anyway. And I'll also make sure to put more sources in my answer next time


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Do airlines need to get approval from manufacturers for procedure deviations?
This question (Why do airlines use their own procedures instead of manufacturers'?) about different procedures with different airlines prompted a followup question from me.  Where deviations occur from the manufacturer's published ones, do they need to get any sort of approval from the FAA or manufacturer to implement these modifications?


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What is this RAF biplane, and where was the photo taken (possibly in the 1920s)?

My grandfather is in the middle row. He joined the RAF as a boy entrant in 1920. He served in Iraq 1924-27 and India 1927-29 so I suspect by the uniforms this is from one of those postings.

I believe the plane is an Airco DH-9A.
https://en.wikipedia.org/wiki/Airco_DH.9A#Interwar_RAF_service

The location may be Iraq. It looks like the RAF 55(B) Squadron: https://en.wikipedia.org/wiki/No._55_Squadron_RAF#Between_the_Wars.
On another picture I think I recognise the dog on the right in your picture (but now a bit older): https://55bomber.wordpress.com/2010/12/02/raf-55b-squadron-hinaidi-iraq/

Blotto:

Wow, that was almost simultaneous :-)

@CamilleGoudeseune I undeleted my answer after adding stuff on the likely(?) squadron. But I do recognise you were first on the plane.

Clever to exploit the dog.  I got nowhere looking for its triangular insignia.

What about the other dog? :-)

@CJDennis didn't even see the black dog! :O Maybe the rapid movement of the white dog drew my attention.

Airco DH.9A. It served during 1920-1931 in the Middle East and India.
Same prop, prop hub, radiator, wing struts, dihedral, exhaust stacks.
I couldn't identify the thing hanging from the top right wing.  Wikipedia's photo has something else hanging there, shaped more like a tiny dinghy than a fuel tank.
I couldn't identify the "triangular roundel" on the radiator, but it matches the one on the side of the nose and on the wing bottom, in Wikipedia's photo.  It may indicate a theatre of operations.

I had the same answer but 1 minute later. I concur. :) However, now you also have to provide the location!

BTW, Wikipedia's first picture shows that same thing hanging from the top wing to the right of the pilot (his right). Whatever it is. Your picture does not. And that triangle sign (in a different location).

Location: in front of a hangar!  Maybe someone who knows military uniforms (or even names to match to faces) could figure out which airbase this was, and when.

Thanks all, and top work on the dog identification! My grandfathers service record shows he was with "M Sqdn" Iraq, then 55 Sqdn Iraq so spot on guys, thank you.